With the introduction of Night Mode on iOS 13, apps can adapt their colors for a darker scheme in low-light conditions. This is perfect for flight deck use at night!
Both HOTCalculator and FlightBriefing has been adapted to take advantage of this. See the example screenshots below. (Note that night mode can be activated and disabled manually or automatically, all is configured by the individual user in the device settings under “Display and Brightness”.)
(Background image and colors are different for all airlines.)